This invention relates generally to the decantation of suspension, and more particularly to a process and apparatus for decanting at temperatures at and above the atmospheric boiling point of the liquid.
Decantation systems of the general type described herein are already known and are often referred to as continuous thickeners. The purpose of such systems is to obtain sedimentation, i.e. gravitational settling of solid particles suspended in a liquid. The settled solid particles are withdrawn at the bottom of the apparatus and the clarified liquid, freed from the solid particles, is withdrawn from the top of the apparatus.
Somora et al U.S. Pat. No. 3,628,667 described a decantation apparatus in the form of a horizontally elongated vessel (Col. 1, lines 66 to 68), of height approximately equal to width, in which a slurry inlet is positioned below the surface of the liquid inside the vessel. The discharge of clarified liquors is by launders located at the surface of the liquid, and a slurry feed enters the apparatus at effectively atmospheric pressure, since it is dispensed from a feed well open to the atmosphere. The basic concept resides in the fact that the suspension to be clarified is distributed in a distribution chamber and loading well evenly over the entire length of the decantation vessel (Col. 2, lines 62 to 64) which is realized by a distributor chamber extending lengthwise of the vessel substantially coextensive therewith in the top section (Col. 1, lines 74 to Col. 2, line 2).
In Casey, U.S. Pat. No. 4,603,000, there is described an apparatus and process for flocculating and clarifying a solid-liquid slurry in a vertically oriented apparatus whose height is approximately equal to its diameter. An inlet for the deaerated and flocculated slurry is provided below the surface of the liquid inside the vessel and below the surface of the mud bed (Col. 2, line 48). Furthermore, the apparatus includes a preflocculating vessel extending into the top, and arranged coaxially with the clarifier tank (Col. 2 to Col 13 line 21). A flocculating agent is added to the slurry as it passes downwardly under laminar flow through a vertical pipe arranged coaxially with the clarifier vessel. The direction of flow then is changed to become upwardly through a lower chamber for the formation of the flocs, and then its direction is changed again to flow downwardly through an annular passage surrounding the lower chamber and finally is introduced below the surface of the mud bed (Col. 3, lines 8 to 21). This apparatus includes a conical bottom section fitted with a slowly rotating rake that grazes the inner surfaces of the lower portion of the vessel. The discharge of clarified liquor is by launders located at the surface of the liquid, and the feed slurry is effectively at atmospheric pressure, since it is dispensed from a feed well open to the atmosphere.
Spetz, German OS 2 212 646, published Aug. 3, 1972, describes a vertically oriented cylindrical decanter of height smaller than the diameter, having inlets for the feed slurry located below the surface of the liquid, just above the upper surface of the mud bed. The exit of clarified liquor is by launders located at the surface of the liquid and the entry of the feed slurry is effectively at atmospheric pressure, since it is dispensed from a feed well open to the atmosphere.
In alumina plants, associated with the production of aluminum, there is a need for an improved system for separating finely divided red mud solids from digestion liquors. It is the object of the present invention to provide a means whereby finely divided solids can be rapidly separated from a slurry at temperatures above the boiling point of the liquid.